Conventionally, there are two main types of methods of geometrically measuring and inspecting a stereoscopic shape, i.e., a method of projecting various light beams to an object to measure and inspect the reflected light with a photodetector and a method in which the object is measured with a camera from plural directions under natural light of general illumination and the inspection is performed by determining the stereoscopic shape from a correlation among plural images.
The former is classified into various kinds by a light projection method, a type of the photodetector, a positional relationship thereof, and the like. In such classifications, as shown in FIG. 11A, there is a method in which a collecting light state of the reflected light by the confocal optical system is detected to search a focal position and thereby the inspection is performed by obtaining height information on the inspection object. In FIG. 11A, the irradiating light emitted from a light source 101 is emitted toward an inspection object 103, i.e., toward an irradiation direction as shown by a dotted line, a light separation mirror 104 transmits the irradiating light, and the irradiating light is collected at a collecting point Pa on the inspection object 103 by a collective lens 121. In the reflected light reflected by the collecting point Pa on a surface of the inspection object 103, the reflected light (incident reflected light) reflected toward an opposite direction to the irradiating direction is incident to the collective lens 121 again, the reflected light is reflected toward a direction orthogonal to the irradiating direction by a light separation mirror 104, and the reflected light is incident to a reflected light collective lens 105. Then, the reflected light passes through a micro hole of a shielding plate 106 while a collecting point Qa is formed in the micro hole of the shielding plate 106 by the reflected light collective lens 105, the reflected light is incident to a photodetector 107, and the photodetector 107 performs the photoelectric conversion of the light intensity into a photoelectric conversion signal output Ia. At this point, there is an optically confocal relationship between the collecting point Pa of the irradiating light collective lens 121 and the collecting point Qa of the reflected light collective lens 105 (that is, the micro hole of the shielding plate 106).
When the inspection object 103 is moved by a moving amount z from the irradiating light collecting point Pa toward the irradiating direction and located at a position of an inspection object 103-1, the reflected light reflected by the surface of the inspection object 103-1 is shown by a broken line, the reflected light collecting point is moved from the point Qa to a point Qa-1 which is close to the reflected light collective lens 105. Therefore, an image size of the reflected light is enlarged on the shielding plate 106, a quantity of the light passing through the micro hole of the shielding plate 106 is decreased in the reflected light collected by the reflected light collective lens 105, and the photoelectric conversion signal output Ia is decreased in the photodetector 107.
FIG. 11B shows a relationship between the moving amount za of the inspection object 103 and the photoelectric conversion signal output Ia of the photodetector 107. The photoelectric conversion signal output Ia becomes the maximum at the position of za=0 where a reflecting point of the inspection object 103 corresponds to the irradiating light collecting point Pa, and the photoelectric conversion signal output Ia becomes less at a position where the moving amount za is separated from zero. That is, the height information can be obtained at the irradiating light collecting point Pa of the inspection object 103 to perform the appearance inspection by moving the inspection object 103 in the irradiating direction or an opposite direction to the irradiating direction (hereinafter referred to as Z direction) to determine the moving amount za at which the photoelectric conversion signal output Ia becomes the maximum.
FIG. 11A shows an example of a method of moving only the inspection object 103. However, when the positions in the Z direction of the collecting point Pa of the irradiating light and the inspection object 103 are changed (hereinafter referred to as Z scanning), the same effect is obtained. It is clear that a method of moving the whole of the optical system while fixing the inspection object 103, which is of the Z scanning method, has the effect similar to the method of moving only the inspection object 103. FIGS. 12A and 12B show other Z scanning methods.
FIG. 12A shows a method in which the Z scanning is realized by moving only the irradiating light collective lens 121 in the optical system in the Z direction to move the irradiating light collecting point Pa to a point Pa−1. The method is useful in the case where the irradiating light incident to the irradiating light collective lens 121 is close to a parallel light. Only the irradiating light collective lens 121 is the moving body and the irradiating light collective lens 121 is usually light, so that high-speed measurement and simplified mechanism are achieved (for example, see Patent Document 1).
FIG. 12B shows a method in which an optical distance da between the irradiating light collective lens 121 and the inspection object 103 is changed by inserting parallel glass 110 havin g a thickness ta and a refractive index nn between the irradiating light collective lens 121 and the inspection object 103, and thereby the irradiating light collecting point Pa is moved to a point Pa−2 to realize the Z scanning. In the method, the plural pieces of parallel glass having the different thicknesses or refractive indexes are sequentially inserted between the irradiating light collective lens 121 and the inspection object 103, a disc in which the plural pieces of parallel glass are arranged is rotated at high speed, and thereby the high-speed Z scanning can be achieved (for example, see Patent Document 2).
Furthermore, there is a method, in which the reflected light from the inspection object 103 is branched into plural light beams by the plural light separation mirrors 104, the photoelectric conversion signal outputs Ia of branched reflected light beams are simultaneously measured to form the optical system equivalent to the Z scanning method by the plural shielding plates 106 and the plural photodetectors 107 which are placed at positions having different distances from the reflected light collective lens 105 in each branched reflected light, and thereby a time necessary for the Z scanning (for example, a time necessary to move the inspection object 103 and a time necessary to move the irradiating light collective lens 121) can be neglected to realize the high-speed Z scanning (for example, see Patent Document 3).
Thus, the height information on the inspection object 103 can be obtained at the irradiating light collecting point Pa by performing the Z scanning in the confocal method. Furthermore, the inspection object 103 is moved in an X direction and a Y direction which are orthogonal to the Z direction and orthogonal to each other, and the position of the irradiating light collecting point Pa is changed in the Y direction with respect to the inspection object 103 (hereinafter referred to as Y scanning) while the position of the irradiating light collecting point Pa is changed in the X direction with respect to the inspection object 103 (hereinafter referred to as X scanning), and thereby a stereoscopic coordinate (positional coordinate) of the inspection object 103 can be obtained to perform the appearance inspection (for example, see Patent Document 1). Similarly the positional coordinate of the inspection object 103 can be obtained to perform the appearance inspection, in the case where the inspection object 103 is fixed while the whole of the optical system is moved in the X direction and in the Y direction, or in the case where the inspection object 103 is moved in the X direction or in the Y direction while the whole of the optical system is moved in the X direction or in the Y direction.
One of means for achieving the high-speed X scanning and Y scanning is a method in which an optical system for scanning the irradiating light is newly provided in the above optical system to realize the X scanning and Y scanning (for example, see Patent Document 4). There is also a method in which multi-point simultaneous measurement is performed in an XY lattice manner by arranging many confocal optical systems including the light sources 101 to photodetectors 107 in the measuring optical system (for example, see Patent Document 5).    Patent Document 1: Japanese Unexamined Patent Publication No. S62-245949    Patent Document 2: Japanese Unexamined Patent Publication No. H9-126739    Patent Document 3: Japanese Unexamined Patent Publication No. H5-40035    Patent Document 4: Japanese Unexamined Patent Publication No. H3-231105    Patent Document 5: Japanese Unexamined Patent Publication No. H9-257440